The invention relates to a method and apparatus for producing short-lived reactive species in a rapid thermal processing (RTP) system.
RTP systems are employed in semiconductor chip fabrication to create, chemically alter, or etch surface structures on semiconductor wafers. In one type of system, an RTP chamber includes a gas manifold, sometimes referred to as a gas showerhead, positioned above the surface of the wafer to provide a flow of a process gas to the wafer surface. Radiant energy from a heat lamp array passes through the manifold, which can be made of transparent quartz, to heat the wafer during processing. Spent process gas can be pumped out through a vacuum port of the chamber.
Completely replacing one process gas with another one typically takes several minutes with a conventional gas showerhead system. For this reason, it is very difficult to rapidly switch from one type of process to another at the surface of the wafer, such as is desirable in creating very thin layers or structures on the wafer surface. Some RTP processes employ highly reactive species, such as atomic species. In conventional systems, these species are created outside the RTP system, for example, with an electric discharge. The reactive species created by such methods must travel long paths to reach the wafer with conventional showerhead systems. Atomic species can also be created with an electric discharge within the RTP chamber, but employing an electric discharge close to the wafer surface also creates a plasma that can be detrimental to the semiconductor devices being formed on the wafer.
According to one aspect of the invention, an apparatus for producing a reactive gas in a processing chamber includes a gas manifold that has walls providing an internal chamber. A first wall includes a side facing a work piece, another side facing the internal chamber, and a plurality of channels extending from the internal chamber to the side facing the work piece. The gas manifold also includes a port for coupling a gas source to the internal chamber such that a gas flowing into the internal chamber through the port flows out through the channels toward a surface of the work piece. An ultraviolet light source is structured and arranged to illuminate the gas flowing through the gas manifold for altering the chemistry of the gas. The gas manifold can include a reflective surface facing the internal chamber for reflecting the ultraviolet light.
The walls of the gas manifold can comprise a window formed of transparent quartz. A second wall can be arranged spaced apart from the first wall and adjacent a heat lamp array, with a side wall joining the first and second walls at their peripheral edges. The ultraviolet light source is structured and arranged to illuminate the gas in the internal chamber through a window region in the side wall, the ultraviolet light being directed between the first and second walls.
According to another aspect of the invention, a rapid thermal processing chamber for processing a semiconductor wafer positioned within the processing chamber includes a transparent window. The window includes a first pane facing the wafer inside the processing chamber, a second pane being adjacent a heat lamp array on the outside of the processing chamber, a window side wall joining the first and second panes at their peripheral edges to provide an internal chamber therebetween, a plurality of channels extending through the first pane from the internal chamber to the inside of the processing chamber, a port communicating between the internal chamber and a process gas source, and a reflective surface facing the internal chamber. An ultraviolet light source is positioned to illuminate process gas flowing through the window with ultraviolet light such that the ultraviolet light alters the chemistry of the process gas. The ultraviolet light source directs the ultraviolet light substantially parallel to the first and second panes, and into the internal chamber such that the ultraviolet light reflects from the reflective surface in a plurality of different directions within the internal chamber.
In both the gas manifold and the processing chamber, the ultraviolet light source can include one of an ultraviolet lamp, a mercury discharge lamp, and a ultraviolet laser. The ultraviolet light source can also include a controller for turning the illumination on and off, and optical elements directing the ultraviolet light from the ultraviolet light source to pass through a transparent window region of the window side wall into the internal chamber. If the ultraviolet light source is a laser, the controller can include a tuner capable of changing the wavelength of the ultraviolet light provided by the laser.
According to yet another aspect of the invention, a method of processing a semiconductor wafer in a semiconductor process chamber includes the steps of providing a flow of a precursor gas species into a gas manifold, illuminating the precursor gas species in the gas manifold with ultraviolet light, wherein the ultraviolet light interacts with the precursor gas species to create a product gas species, and flowing the product gas species through a plurality of apertures in the manifold towards the wafer in the processing chamber. The illuminating can include reflecting the ultraviolet light off a reflective surface of the manifold so that the ultraviolet light passes through the gas manifold more than once, thereby increasing the interaction with the precursor gas species. The processing can be controlled by controlling the illuminating.
The gas manifold can include a transparent window, and the method can further include the step of heating the wafer by shining radiant energy from a heat lamp array through the window.
The product gas species, which is non-ionic and will typically be more reactive than the precursor gas species, can include nitric oxide, ozone, an atomic species, or any other gas species that can be produced by illuminating a precursor gas species with ultraviolet light. The product gas species can be a reactive gas species having a half-life of about a minute or less.
According to still another aspect of the invention, a method of controlling a process in a semiconductor processing chamber includes the steps of flowing a first gas into an internal chamber of a gas manifold and thence through apertures of the manifold toward a semiconductor wafer in the processing chamber, controlling an ultraviolet light source to illuminate the first gas within the gas manifold with ultraviolet light, wherein the ultraviolet light interacts with the first gas to produce a second gas which comprises a non-ionic species, and flowing the second gas through the apertures toward the semiconductor wafer. The method may further include stopping the flowing of the second gas by controlling the ultraviolet light source to stop illuminating the first gas within the gas manifold. The method may also include heating the wafer by shining radiant energy on the wafer through the gas manifold.
An advantage of the invention is that it provides a wafer processing method and apparatus for producing highly reactive chemical species, including atomic species, from less dangerous, less reactive, and longer-lived precursors. A further advantage of the invention is that the process does not produce ionic species, and therefore reduces the risk of damaging the semiconductor devices being formed on the wafer with such species.
Many of the reactive species formed according to the invention are short-lived, and therefore do not pose a disposal or storage problem. The short-lived species can be produced and delivered to the surface of a wafer in large enough quantities to enable faster processing. By multiply reflecting the UV light within the gas manifold, the precursor gas species is exposed to a higher intensity of UV radiation than would otherwise be available from the same source. This produces greater quantities of reactive product gas species in less time than with systems that do not employ multiple reflections. When processing with short-lived species according to the invention, turning the ultraviolet light on and off starts and stops the flow of the reactive species to the wafer in much shorter time periods than could be achieved with prior art systems, which feature allows for precise process control and rapid switching between processes.